The free solution conformation of peptides serves as a logical starting point for delineating this conformation-activity relationship. Limitations of existing methods of NMR spectroscopic conformational analysis of peptides point to the need for developing new and more reliable methods. Using the peptide hormones oxytocin as a model, we propose to determine its conformation in aqueous and dimethyl sulfoxide solution by means of intramolecular and intermolecular nuclear Overhauser effect (NOE) measurements and by NMR experiments involving binding of paramagnetic lanthanide ions to a derivative of oxytocin (ONTO) which is nitrated on the ortho-position of the tyrosine side chain. These methods have been applied to small organic molecules and in some cases also to proteins. Adaptation of these techniques to peptides is the principle objective of this study. Specifically, it is proposed 1) to develop a method for the quantitative measurement of NH proton exchange rates by solvent saturation experiments in H2O using a combination of Fourier transform and correlation NMR spectroscopy, 2) to develop a method for quantitative or semiquantitative estimation of the exposure to solvent of aromatic CH protons by intermolecular NOE experiments in H2O, 3) to analyze the intramolecular NOE data for oxytocin and the paramagnetic shift and relaxation data for ONTO in terms of specific models proposed for these molecules. The following considerations led to the choice of oxytocin as the model for these studies: 1) the availability of extensive data on this hormone permits one to focus on new methods without the necessity of repeating routine experiments; 2) this laboratory has considerable experience in the study of this peptide; and 3) our collaborator, Dr. Roderich Walter, has available or can prepare various analogs required for this investigation. Determination of the solution of oxytocin is incidental to this study. The chief objective is development of techniques of general utility to determination of peptide conformations. We fully recognize that oxytocin has been extensively studied in this and other laboratories.